Transparent polyolefin films of high modulus and clarity



March 31, 1970 R. F. WILLlAMS, JR, ETAL 3,5

TRANSPARENT POLYOLEFIN FILMS OF HIGH MODULUS AND CLARITY- Original Filed July 14, 1966 \INVENT A TTORNEXS' ROBERT E W/LL/AMS,JR. R/CHAPD H JEN/(5 United States Patent 3,503,843 TRANSPARENT POLYOLEFIN FILMS OF HIGH MODULUS AND CLARITY Robert F. Williams, Jr., Webster, and Richard H. Jenks,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Application July 14, 1966, Ser. No. 565,305, which is a continuation-in-part of application Ser. No. 197,217,

May 7, 1962, which in turn, is a continuation-in-part of application Ser. No. 9,567, Feb. 18, 1960. Divided and this application Oct. 16, 1967, Ser. No. 683,064

Int. Cl. B32]: 27/32 US. Cl. 161165 7 Claims ABSTRACT OF THE DISCLOSURE Increased stiffness and better clarity of polymeric films can be obtained by compression rolling relatively thick films of the polymers, provided that the films are coated (at the juncture of the rolls with the film) with enough liquid lubricant to form a hydrodynamic wedge in the nip area. Films having higher modulus and greater clarity (than could otherwise be produced) can be manufactured by this process. Polyolefin films having such higher modulus plus excellent clarity (less than 3% haze) are claimed.

This application is a division of United States patent application Ser. No. 565,305, filed July 14, 1966 (now abandoned), which in turn was a continuation-in-part of United States patent application Ser. No. 197,217, filed May 7, 1962 (now abandoned), which in turn was a continuation-in-part of United States patent applications Ser. No. 9,567, filed Feb. 18, 1960 (now abandoned); Ser. No. 16,208, filed Mar. 21, 1960 (now abandoned); and Ser. No. 30,324, filed May 19, 1960 (now abandoned). Application Ser. No. 16,208 was a continuationin-part of US. patent application Ser. No. 833,666, filed Aug. 10, 1959 (now abandoned) which, in turn, was a continuation-in-part of US. patent application Ser. No. 706,626, filed Jan. 2, 1958 (now abandoned).

This invention relates to the fabrication of strong, clear, transparent film in sheets from organic polymeric thermoplastic film.

Sheeting made from synthetic organic thermoplastic materials has found considerable utility for packaging purposes, photographic film base, and the like. However, it has been desired to have improved stiffness and clarity for many of these polymeric films. In addition, it has been desirable to incorporate into the polymeric materials one or more of a large number and types of additives such as stabilizers, antioxidants, ultraviolet absorbers, slip agents, antiblocking agents, moisture-proofing agents, and the like.

Various methods are known for improving the physical characteristics of polymeric film; for instance, the material may be extruded into a quench bath. Some films may be stretched in one or both directions and still others may be calendered using heated rolls above the softening temperature of the polymeric film. However, the clarity of some of these films has not been satisfactory for many purposes, and it has been desirable to find a method of improving the clarity. Moreover, the stretching method tends to enlarge any pin holes or voids which may be existing in the polymeric film as originally prepared. This further decreases the moisture-barrier properties of the film and decreases its usefulness for packaging purposes.

The addition of additives to polymeric materials usually occurs prior to the extrusion step or solution step if the film is to be cast. The additive is added to the polymer and incorporated throughout the resulting structure. Therefore, it is necessary to know before preparing the initial film what additive or additives are to be added to the polymeric film. This necessarily reduces the ability of the manufacturer to add additives once a film strip has been prepared, and it has been desired to find a method of adding various agents to the film depending upon its ultimate use after the film has been extruded or cast. Moreover, it has been determined that most of the additives in polymeric film exert their beneficial effect at the surface of the film. Accordingly, it is preferable to have the additive located solely at the surface of the film if this were conveniently possible, not only to increase the efi'ectiveness of the additive but to decrease the quantity of the additive required which would not be needed in the interior of the film.

We have found a method of compression rolling polymeric film formed by either extrusion or cast-coating which improves 1) the clarity of the film, (2) the moisture-barrier properties, (3) the stiffness as measured by Youngs modulus, and (4) the tensile strength as well as other mechanical properties. We have also found a method of incorporating additives in the surface during the compression-rolling operation.

One object of this invention is to provide a method for compression rolling polymeric materials at lower pressures and/or temperatures than used previously for obtaining the same thickness reduction. An additional object is to provide a process of compression rolling polymeric materials using lubricants. A further object of this invention is to provide a method of improving the crystalline structure or orientation of the molecules in polymeric films. Another object is to provide polymeric materials which have additives incorporated in the surface of the polymeric films. An additional object is to provide a method of incorporating various additives into the surface of polymeric films.

The above objects are obtained by compression rolling the polymeric film under specific operating conditions. The polymeric sheeting is passed between rollers having a pressure sufficient to decrease the film to one-half to one-tenth in thickness. A lubricant is used on the polymeric film as it passes through the nip between the two rollers. This lubricant can be applied to either the polymeric sheeting directly or placed on the rollers so it is transferred to the polymer as it passes between the rollers. The temperature of the pressure rollers depends on the density and the softening temperature of the polymer. For most polymers, the temperature can be at room temperature, but it may be varied from 40- 300 F. depending upon the polymer.

By a lubricant is meant a liquid or material that acts as a liquid in the area Where pressure from the rolls is applied to the film. The lubricant in this case acts to form a full or partial fluid film between the roll and the polymeric film. Thus, the roll surface and polymeric film are separated by the liquid lubricant which prevents contact and increases mobility as the film enters the nip. This fluid film formation is based on the hydrodynamic theory for bearings. The theory and experimental data prove that by applying a copious supply of lubricant with the proper geometry and sufficient speed a hydrodynamic wedge or film is formed. This results in effectively reducing the nip or load area which results in higher unit stresses for a given load. Thus the effective peak pressure generated in the nip is increased by the hydrodynamic eifect over that which would be expected by elastic theory.

This type of lubrication deviates from the common or conventional boundary type where a lubricant, liquid or solid, is impregnated or applied to the polymeric surface.

Conventional lubrication is based on the theory of boundary lubrication which effectively reduces friction in the range of m,u=.2 or .3 to III/1.2.1 to .15. The claimed unique method of producing a hydrodynamic film results in coefficient of friction values in the order of In,u.:.00l. This reduction in friction has minor effect in reducing dry skidding and heat generation. The major effect of using a hydrodynamic wedge is in its ability to effectively reduce the area under load, thus with the same total load create a much higher unit pressure.

In the event that water is used as a lubricant, it is desirable to add a wetting agent such as Aerosol OT which is dioctyl sodium sulfosuccinate. A sufficient amount of the lubricant is used to cover the surface of the polymer as it passes between the rolls, The application may be by spray, wick, immersion coating, etc. Methods of insuring surface coverage may be used such as air knife, bar, wick, and the like. The lubricant which may be used must be an inert material which will not adversely affect the finished product, and it should preferably wet the surface sufficiently to cover the surface at the point of pressure during the compression-rolling operation. The additives, if desired, are incorporated into the lubricant and the lubricant is chosen so that it will form a solution of the additive in our preferred embodiment, although emulsions or suspensions can be used, particularly when the additive is an inorganic solid such as silica or the like.

In the event that a particular organic chemical were to be used as an additive, it might be dissolved in a solvent such as ethyl alcohol or the like and used as a lubricant. Various solvents may be combined to form a suitable lubricating mixture which will satisfactorily dissolve the additive and incorporate it into the surface of the film.

A group of antioxidant compounds suitable for use as additives to polyolefins according to our invention include phenolic compounds. This group includes: phenol; alkylphenols, such as 2,4-dimethyl 6 tertiarybutylphenol and 2,6-ditertiarybutyl 4 methylphenol; cc naphthol; dihydroxynaphthalenes, such as 1,5- and 1,7-dihydroxynaphthalenes and the monoalkylethers thereof; 1-hydroxy-4- alkoxy-S,S-dihydronaphthalene; catechol and alkyl cate chols including nordihydroguiairetic acid; dihydroxybenzene, such as hydroquinone, and alkyldihydroxy benzenes and monoalkylethers thereof, such as Z-tertiarybutyl-4-methoxyphenyl; trihydroxybenzenes such as pyrolgallol and alkylpyrogallols; alkyl gallates; 2,2-dimethyl- 5-hydroxy-6-tertiarybutylcoumaran; and 2,2-dimethyl-6- hydroxy-7-tertiarybutylchroman. It can be seen that the phenolic compounds may be mono or polynuclear and may contain one or more hydroxyl groups (that is to say they be monoor polyhydric phenols) and substituted hydroxyl groups such as alkoxy substituents.

Another group of organi antioxidant compounds particularly suitable for adding in accordance with this invention comprises p-substituted anilines wherein the psubstituent is selected from the group consisting of hydroxyl, amino and alkylamino radicals, e.g., p-aminoanilines and p-hydroxyanilines. This group of compounds may be further classified as p-substituted-N-alkylanilines wherein the p-substituent is selected from the group consisting of hydroxyl, amino and alkylamino radicals such as p-amino-N-alkylanilines; p-alkylamino-N-alkylanilines; and hydroxy-N-alkylanilines. This group of compounds includes p-sec-butylamino-N-sec-butyl-aniline, p-hydroxy- N-methylaniline, p-n-butylamino-Nn-butyl-aniline, and o-methyl-p-sec-butylamino-N-sec-butylaniline.

The foregoing and similar organic antioxidant compounds may be used individually, and also two or more of these organic compounds may be used together.

The following may also be used: synergistic stabilizer combination comprising a 4-alkoxy-2-hydroxybenzophenone and a diester of beta, beta-thiodipropionic acid as disclosed in U.S. Patent 2,972,597 issued Feb. 21, 1961 and U.S. Patent 2,861,053 issued Nov. 18, 1958; a synergistic stabilizer combination comprising a 4-alkoxy-2-hydroxybenzophenone and a zinc N,N-dialkyldithiocarba mate as disclosed in U.S. Patent No. 2,972,597 issued Feb. 21, 1961; a synergistic stabilizer combination comprising a 4-higher alkoxy-2-hydroxybenzophenone and an alkylene-bis-phenol of the group consisting of 2,2- methylene-bis(4-methyl-6-(l methylcyclohexyl)phenol) and 4,4-ethylene-dioxybis(2-tertiarybutylphenol) as described in U.S. Patent 2,976,260 issued Mar. 21, 1961;

a synergistic stabilizer combination comprising a 4 alkoxy-2-hydroxybenzophenone and N,N'-diphenyl pphenylencdiamine as described in U.S. Patent 2,947,721 issued Aug. 2, 1960; a stabilizer combination comprising resorcinol monobenzoate and 2,2'-methylenebis(6-tertiarybutyl-p-cresol) as described in U.S. Patent 2,983,709 issued May 9, 1961; a stabilizer combination comprising a tris-(dialkylamino) phosphine oxide and a 2-hydroxy- 4,4'-dialkoxy-benzophenone as described in U.S. Patent 3,003,996 issued Oct. 10, 1961; a stabilizer combination comprising 2,2-methylenebis(6 methylcyclohexyl pcresol) and a 2-hydroxy-5-alkylbenzophenone as described in U.S. Patent 3,000,856 issued Sept. 19, 1961, and a mixture of copper stearate and p-tertiarybutylphenol.

Agents which may be incorporated in the surface of polyolefin materials include those which are finely-divided solids. For instance, these may be silicas, aluminum hydroxide, talcum powder, ground glass, titanium dioxide and the like. Various concentrations may be used and the solid material may be used in the form of a dispersion. Varying degrees of fineness may be used for solid materials, but colloidal size is preferred. The incorporation of finely-divided solid material into the surface of polyolefins improves the adhesion of coatings on the polyolefin surface and also improves its ability to retain printing and the like. Other agents which may be incorporated by adding to the lubricants during compression rolling, include slip agents, such as various polymeric materials, which can be added to the lubricating agent. Typical of these are aliphatic and aromatic amides, preferably of 12-25 carbon atoms, i.e., stearamide, or the like. Commercially available slip agents such as Armid-O may be used.

Antiblocking agents may also be added as well as moistureproofing agents. Typical antiblocking agents include diatomaceous earth, ethylene distearamide, and the like. Typical moistureproofing agents include microcrystalline wax and paraffin wax. In many instances, the additives which are used may accomplish more than one purpose. For instance, the use of talc as an additive may not only provide a slip agent or antiblocking agent but may also improve the surface so that it has improved the adhesive properties.

Many other additives are known in the art and these can be also incorporated into the surface of a polymeric film in a similar manner. It would not be feasible to list every known additive, but the ones shown herein are typical of those which may be added by combining with a suitable lubricant for use in compression rolling of polyolefins. In some instances, the additives may be prepared in the form of an emulsion and suitably added by using the emulsion as a lubricant.

Several additives may be used in combination depending upon the ultimate use of the polyolefin sheeting.

Polymers such as polyolefins which may be further improved in the processing characteristics by quenching the molten polymer are first heated to obtain a clear melt and then extruded through a suitable die to obtain a film of the desired thickness. The film may then be quenched by passing it into cold water or else onto a chilled cold roll so that the polymer is solidified and cooled rapidly during contact with the support to a temperature far enough below its recrystallization temperature to avoid clustering of crystals or excessive formation of spherulites. The cooling liquid could be as warm as 210 F. and could be cooled down to about 65 F. de

pending upon the melting point of the polymer and the size of the cooling medium.

Polyolefins may be compression rolled which are substantially crystalline selected from those polyolefins obtained by polymerizing an a-olefin having 21O carbon atoms or copolymers of these u-olefins.

Polyolefins which are within the scope of our invention include polyethylene and polypropylene which are substantially crystalline and also blends of polyolefins, polyolefins such as poly-4-methylpentene-l, poly-3-methylbutene-l, polyallomers and related homologs.

The propylene-olefin polyallomer is a normally solid, crystalline polymer prepared as by first polymerizing propylene to form a crystalline, propylene polymer and then copolymerizing said propylene polymer with another a-olefin having 2-10 carbon atoms until the. resulting product has an olefin content of as much as 20% by weight.

In compression rolling polyethylene, we use a polyethylene having a density of .910 to .975 g./cc. obtained in a sheet 2-10 times the thickness which is desired in the finished sheet. The polyolefin sheeting is passed between rolls having a pressure sufficient to decrease the film /2 to in thickness. The temperature of the pressure rolls depends on the density and the softening temperature of the polyolefin; for polyethylene, the temperature preferably would be in the range of 40240 F.; for polypropylene, 40285 F., preferably l00270 F.

Various methods of heat treating the polymer sheeting may be used such as surface winding on a take-up roll and then heating the roll in an oven. However, temperature and time relationships can be balanced; for example, a higher temperature relaxing the film in a shorter time. The temperature at which the film is relaxed must be approximately the creep or distortion temperature of the particular polymer and must be lower than the fatigue temperature of the polymer. By fatigue temperature, 'as used herein, is intended the temperature at which the tensile strength of the polymer is between 14 and pounds per square inch. The creep or distortion temperature is the temperature at which the length of a test specimen is increased or decreased 2% of its original length, when the test specimen is supporting a linear load of 10 grams per square millimeter and the temperature is being increased at the rate of 10 C. per minute.

By using a lubricant in compression rolling, we can obtain an improved modulus and transparency for a thicker film than can be obtained using the same type of polymer without a lubricant. Additional improvements obtained by using a lubricant include a clearer film than is obtained under similar conditions without using a lubricant. The pressure required is not as high to obtain the same reduction and thickness. Moreover, static charges are reduced in the rolling operation and may be completely eliminated. Film may be rolled flat for certain uses such as packaging without the need for a separate step of heat treatment. Irregularities in the film thickness or gauge are not as critical when lubricants are used as when film is rolled dry. The roll finish is not as critical for obtaining surface gloss with lubricants since scratches or imperfections will be filled or covered by the film of lubricant which covers the rolls.

The rate at which the film is rolled by the pressure roll is not critical, since satisfactory films can be produced at speeds from 2 /2 feet per minute upwards to about 1700 feet per minute.

Various polymeric materials may be used in our process including polyesters such as polyethylene terephthalate, polyamides (nylon), polycarbonates, chlorinated polyethers, polyacetals, cellulosics, such as cellulose acetate, cellulose propionate, cellulose butyrate and the like, halogenated polyolefins such as polytetrafiuoroethylene, etc.

Lubricants that might be used would be hydrocarbons such as xylene, VMP naphtha, esters such as butyl acetate,

alcohols such as butanol, ethers such as diethyl Cellosolve, alcohol-ethers such as 2-ethoxyethanol, ketones such as methylisobutyl ketone, glycols such as ethylene and diethylene glycol, water with and without a wetting agent, parafiin or parafiin emulsions, low-molecular weight polyethylene waxes and the like,

The same set of rollers can be used for compression rolling multiple strips of polyolefin sheeting for obtaining two or more compression rolled strips at the same time.

In order to compression roll multiple strips, two or more sheets of the polymer are fed into the compression rolls having a lubricant covering the surfaces of the polymeric sheeting as it contacts the rolls at the nip. When the sheets have similar chemical compositions, the lubricant must also cover the surface of the polymeric sheeting where it contacts another similar surface to avoid obtaining adhesion of the strips to each other. However, if the chemical composition of the sheets is dissimilar enough, such as polyethylene rolled with polypropylene; no lubricant is required between the dissimilar sheets.

The multiple rolling process is particularly adaptable to compression rolling lay-flat tubing. This tubing can be prepared by methods already known in the art. However, in our preferred embodiment, the polymeric tubing, such as polypropylene, is prepared by dry extruding seamless tubing into a water bath where the tubing is inflated with a liquid having a higher density than water before running the tubing through pinch rolls.

The gauge of the tubing is determined by the liquid level inside the tubing, the density of the liquid, and the draw-down between the die and the pinch rolls. This process is particularly useful for polypropylene since an improved product is obtained when the lateral stretching of the polypropylene occurs at the time it is quenched. The process of compression rolling multiple strips is set forth in United States Patent No. 3,194,863 to Williams et al.

The accompanying drawing illustrates one embodiment of our invention.

The polymer 3 in this embodiment is extruded from the extruder 1 through the die lip 2, onto a chilled roll 4, around the idler roller '5, through the tension rollers 6 and 7, and between the pressure rollers -8 and 9, at which point the polymer is reduced in thickness to nineteen-twentieths to one-tenth of the thickness as extruded. liext the polymer passes around the idler roller 10 to relaxing roller 11 which is heated to about 200 F., past the idler roller 12 and around the chilled roller 13 to take-up 14. All the rollers are similarly supported except for the pressure roller which requires a heavy support. Lubricants are applied through nozzles 15 associated with the plate 16 connected to the lubricant.

With certain of the polymeric materials the polymer maybe reduced to clear melt by feeding pellets of the polymer between two heated rollers until the polymer reaches a molten state and then passing it through a series of rollers in a similar manner as described above. With others such as the cellulose esters, polycarbonates, etc., films may be prepared by casting a dope on a polished surface.

It will be apparent to one skilled in the art that the position of the rollers may be changed from horizontal to vertical and they may be arranged in various positions relative to each other, such as in the S or Z position. The idler rollers are used to facilitate transfer of the polymeric sheeting without large heat transfers from the rollers which are maintained at certain temperatures.

The following examples are intended to illustrate our invention but not to limit it in any way:

EXAMPLE 1 The following table shows examples of polymeric materials which have been compression rolled according to our invention.

Various additives which are soluble in methanol and ethylene glycol are added to the lubricant prior to the Modulus, 10 p.s.i. MIT folds Elmendoi'f tear, g. Roll Percent Sample Lubricant temp., F. extension Length Width Length Width Length Width Polyester- Diethylene glycol. 200 194 6. 2. 2, 000+ 2, 000+ 848 192 Cellulose tri Aerosol OT soluti 150 6 5. 7 5. 7 46 50 48 48 Parai'lin emulsion* 150 23 6. 5. 5 37 58 25 23 Xylene 220 12 5. 6 5. 4 21 43 45 48 Check, not calendered 4. 7 5. 8 39 51 64 63 Parafiin emulsion, 4 g. paraffin, 4 g. aerosol OT, 500 ml. water, 200 ml. isopropanol.

EXAMPLE. 2

A sheet of high density polyethylene having a density of .962 g./cc. was prepared as described in Example 8 having 60 mils thickness and also drawn perpendicular to the direction of extrusion at 100 F. to a thickness of 25 mils (140% extension). It was then pressure rolled parallel to the direction of extrusion at 240 F. to a thickness of 5 mils (400% extension). The film was Wound to prevent any elastic recovery in either direction and heated for 30 minutes at 240 F. The modulus of the finished film was 4.0 to 4.5 X 10 pounds per square inch. The percent scattered light was less than 3% and the creep temperature was above 240 F.

EXAMPLE 3 In the following table, results are shown for the percent extension obtained with polyolefins when rolled EXAMPLE 4 The followingtable gives a comparison of properties of polyolefin films obtained by pressure rolling using lubricants and without lubricants. The minimum roll temperatures for obtaining the required extension with dry rolling and with lubricants was determined to eliminate the visual haze in the original films. The samples with a lubricant and without a lubricant. Methanol was were extruded as in Example 13.

I Relaxed Comparison of properties of polyolefin films by lubricating Temp, hour and dry rolling F. 2'7 under distortion suflicient MV T R Film Percent Elmenunder tension to grams thickness Tot dorf Modulus. p.s.i. load prevent per 100 Roll Percent (mils) scattered tear (10 (relaxed shrinkage in. per Roll procedure temp., F extension light (grams) p.s.i.) film) F. 24 hrs.

(1) Medium density polyethylene:

Lubricated (MeOH) 80 304 1- 2 1- 11 8 1- 4 194 220 0. 11 Dry 120 304 l. 2 3. 17 176 0. 8 192 220 (2) Phillips process hi-dcrisity polyethylene:

Lubricated (HzO/Aerosol O.T.) 80 403 2. 2 2. 48 32 2. 5 237 239 0. 11 Dry 150 392 2. 2 3- 07 48 2. 2 232 239 0. 11 (3) Ziegler process hi-density polyethylene:

Lubricated (HzQ/Aerosol O.T.) 80 376 2. 2 2. 56 16 2. 2 217 239 0. 10 Dry 160 376 2. 2 3- 27 16 2. 2 223 239 0. 13 (4) Polypropylene:

Lubricated (ethylene glycol) 200 376 2.3 1. 84 16 2. 0 266 284 0. 25 Dry 240 377 2. 2 3 49 16 3.4 245 284 0.24

No'rE.All physical properties in the above table were determined on films in the direction parallel to that of extension by rolling, except for seattcred light and MVTR.

MVTR represents Moisture Vapor Transmission Rate.

used as the lubricant for polyethylene; ethylene glycol was used for polypropylene.

The minimum percent extension using a lubricant was determined which was required to eliminate the visual haze in the original films. The pressure required to obtain the minimum percent extension using a lubricant which eliminated visual haze was determined for each resin. Films were then compression rolled with and without lubricant at thse pressures. Roll temperatures were 80 F. for polyethylene and 200 F. for polypropylene. Each sample was extruded from a clear melt. One and three were extruded onto a chilled roll. Two and four were extruded into a quench bath.

Percent extension EXAMPLE 5 Haze and extension determinations as follows were made on medium density polyethylene (0.93 g./cc.).

. Films were pressure rolled at a roll temperature 80 F.

using film extruded from a clear melt onto a chilled roll.

for medium density polyethylene (0.93 g./cc.) extruded as in Example 5.

Roll With Without Polyolefin teinp., F. lubricant lubricant Thickness I Roll ori rial P t 1 M d d t h g1 Green :2; 11313518111? yiilpflilyetuylenel 304 83 7 Lubricant temperature mils extension iensi ypo ye y erie Iso ro lal h 1 Phillips Type (density 0.96).. 80 403 213 Pet iol uhn oil 3 5 (3) Eli-density polyethylene Methyl ethyl ketone 80 30 31 (4) P llieglegs'llype (density .955). 2%; 376 84 Oyclohexane 80 30 378 0 r0 ene 76 196 1,2,3 4 1 t .h d- C (5) Low density (density 0.920) 80 355 104 7 Methyl rilc o liolu f jf i i fi iFj: o

9 EXAMPLE 7 The following determinations show the relationship between polyethylene samples of varying densities of samples pressure rolled using methyl alcohol as a lubricant. The polyethylene was extruded as in Example 5 with no appreciable drawdown and the samples were not heat treated.

MV TR, Modulus g./100 infl/ Density Haze Thickness above 24 hrs.

. 91. 929 Less than 3% 2. 5 1. X10 20 93-. 945 Less than 3% 2. 5 2. 0X10 946-. 97 Less than 3% 2. 5 2. 5X10 l0 EXAMPLE 7A Length Width Tensile strength at break (lbs/sq in 13, 700 15, 200 Elongation at break, percent". 20. 2 24. 3 Modulus (lbs/sq. in.) 3. 5X10 3. 5x10 Elmendorf tear (g.) 23 '26 Haze 2. 0 2. 0

EXAMPLE 8 A propylene polyallomer containing ethylene. and having a density of 0.906 g./cc. and a flow of 1.38 at 230 C. using a 2160 g. load was extruded from a 1 /2" Modern Plastics extruder as five mil strip. The melt temperature of the polyallomer entering the die of the extruder was 225 C. The lips of the extruder die were set mils apart and the strip was drawn down to 5.6 mil. before 10 EXAMPLE 9 A propylene polyallomer containing butene-l having a density of 0.913 g./cc. and a flow rate of 2.0 at 230 C. using a 2160 g. load was extruded as strip. This polyallomer was extruded at a melt temperature of 223 C. into a 24 C. Water bath as strip 5.9 mil thick. The strip was compression rolled between polished steel rolls heated to 127 C. using a 10% ethylene glycol/90% water lubricant to 1.3 mil film.

Physical properties determined on the compression rolled film were:

Moisture vapor transmission (grams/100 sq. in./

24 hr.) 0.40 Lemon oil permeability (grams/ 100 sq. in./

24 hr.) 1.44 Percent haze 2.32

MIT Folds:

Length 500+ Width 500+ Tensile at yield, 10 p.s.i.:

Length 35.0

Width 5.3

Elongation at yield percent:

Length 38 Width 4.8

Modulus, 10 p.s.i.:

Length 4.8

Width 2.4

EXAMPLE 10 Blends were prepared of a high density polyethylene resin having a density of 0.96 g./ cc. and a low density polyethylene resin having a density of 0.925 g./cc. by mechanically mixing the pellets of the. compositions prior to extruding. These blends were extruded as strip onto a chill roll, then compression rolled in a two-roll Fenn Mill using a .03% Aerosol OT/ water solution as the lubricant.

Conditions for rolling and physical properties determined on the compression rolled films were:

Composition Percent Percent Modulus, 10 5 p.s.i. Moisture vapor, high density low density Roll temp., Percent roll transmission, polyethylene polyethylene 0. down Percent haze Length Width g. /100 in./24 hr.

being quenched in a 24 C. water bath located four inches 50 EXAMPLE 11 from the extruder die lips. The extruded and quenched strip was compression rolled using a 10% ethylene glycol/ 90% water lubricant between polished steel rolls heated to 127 C. The thickness of the strip after one pass between the rolls was 1.2 mil. Physical properties determined on the film after compression rolling were:

Moisture vapor transmission (grams/ 100 sq. in./

24 hr.) 0.53 Lemon oil permeability (grams/ 100 sq. in./

MIT Folds:

Length 500+ Width 500+ Percent Haze 2.7

Tensile at yield, 10 p.s.i.:

Length 33.6 Width 3 8 Elongation at yield percent:

Length 30.7 Width 5.8

Modulus, .10 p.s.i.:

Length 3.3 Width 1.7

A strip of polyethylene terephthalate was extruded and quenched to produce an amorphous structure. The amorphous strip was tentered to 3 times its original width then compression rolled to 3.5 times its original length. The tentered strip was compression rolled at 127 C. using a 20% ethylene glycol/ water lubricant. Modulus values determined in three directions were:

Direction of Sample: Modulus, 10 p.s.i.

Length (compression rolling direction) 6.6 Width (tentering direction) 6.1 Diagonal (45 to length and width) 6.2

EXAMPLE 12 A polycarbonate resin having an intrinsic viscosity of 1.12 in methylene chloride at 25 C. was plate coated as a film from a 1,1,2-trichloroethane dope of the resin. X-ray difiraction patterns of the cured film indicated the structure was crystalline. Percent haze of the film as cured was 27.3. This film was compression rolled from a thickness of 4 mils to 2 mils between rolls heated to 104 C. using a 0.03% Aerosol OT/water lubricant. Percent haze of the compression rolled film was 6.0.

EXAMPLE 13 A polycarbonate resin (intrinsic viscosity in methylene chloride of 1.45) plasticized with 10 parts triphenylphosphate was coated on a coating wheel from a methylene chloride dope. The coated and cured film was 5.4 mils thick and the percent haze was 21.4. This film was compression rolled to a thickness of 3.45 mils between rolls heated to 110 C. using ethylene glycol as a lubricant. Percent haze of the compression rolled film was 5.5.

EXAMPLE 14 A melt of polyhexamethylene adipamide was extruded from a 1% inch Modern Plastic extruder as five mil film. The take-01f equipment for removing the film as it was extruded was a water tank and a Fenn Mill compression roll assembly. The tank was filled with a water quenching bath. Thus, the extruded five mil film of polyhexamethylene adipamide entered the water bath where it was quenched and then was fed directly from the bath into the nip between the two 10 /2 inch diameter polished steel rolls of the Penn Mill and reduced in thickness to 1.62.0 mils. The percent haze determined on the film after compression rolling was in excess of 12.

It is believed that the poor haze factor possessed by the compression rolled polyhexamethylene adipamide film is directly attributed in large measure to the fact that the film was not evenly covered by the water carried thereon. A visual inspection of the polyhexamethylene adipamide film leaving the water bath and entering the compression roll assembly revealed that the water tended to puddle or otherwise run off the film prior to its reaching the roller nip.

EXAMPLE 15 A melt of polyhexamethylene adipamide was extruded from a 1% inch Modern Plastic extruder as five mil film. The take-off equipment for removing the film as it was extruded was a roll take up assembly. Thus, the extruded five mil film of polyhexamethylene adipamide was solidified while being conveyed through room temperature air and was then wound. The wound polyhexamethylene adipamide was then compression rolled between the two 10 /2 inch diameter polished steel rolls of a Fenn Mill to a thickness of 1.1.6 mils. A standard Stoddard solvent was placed on both surfaces of the five mil film just prior to its entering the nip of the rolls. Since the Stoddard solvent is not absorbed by the polyhexamethylene adipamide film but rather spreads evenly over the surface of the film, it acts as a lubricant within the meaning of the term as used in this invention. The percent haze of the film that had been compression rolled with Stoddard solvent as a lubricant was 0.9-1.0.

Thus, by comparing the results of this example with that obtained under the conditions set out in Example 14, it can be seen that acceptable results can be obtained only when the film is evenly covered with a lubricant.

EXAMPLE 16 A section of the roll of five mil polyhexamethylene adipamide film that had been extruded into air and wound in the manner set forth in Example 15 was compression rolled in the Penn Mill, and reduced in thickness to 1.6- 1.7 mils using Aerosol OT/ water lubricant applied to both sides of the film. The percent haze determined on the dry film compression rolled with the Aerosol OT/water surface lubricant was 2.6.

EXAMPLE 17 A hygroscopic polymer in the form of nylon was soaked in water for 24 hours at 75 F. After being removed from the water bath, the surface of the sheet was wiped free of surface water and weighed. The gain in weight determined was 7.47%. A similar sheet of polyethylene was also soaked in water for the same period of time under the same conditions. The gain in weight was 0.03%.

Sheets of nylon were compression rolled using water as a lubricant. The polymeric sheets had not been soaked in water and the lubricant was applied to the surface of the sheets at the point of pressure between the compression rolls.

The following table shows the comparison between the compression-rolling operation using a lubricant and compression rolling the films directly after soaking in water for 24 hours:

The roll pressure used with all the samples was the maximum that could be obtained on a No. 102 Penn Mill equipped with rolls 10 inches in diameter. Those results illustrate the difference in the effect of internal plasticization and surface lubrication on compression rolling of nylon.

EXAMPLE 18 Spencer type 401 nylon was extruded from a 1% inch Modern Plastic extruder as five mil film. The take-off equipment for removing the film as it was extruded was a tank and roll assembly. The tank was filled with 60 F. water until it was within six inches of the extruder die lips. A roll of film was then extruded and left submerged in the tank filled with water for twenty-four hours. After the film was soaked for twenty-four hours, it was removed from the tank taking all possible precautions to prevent removing any water that adhered to the surface of the film. This soaked film was compression rolled immediately after removal from the tank between two 10 /2 inch diameter polished steel rolls in a Penn Mill and reduced in thickness to 1.5-1.6 mils. The percent haze determined on the film after compression rolling was 8.711.1.

Thus it is readily seen that the same haze factor is produced in a nylon film whether its surface has all the water thereon that it will carry, as is the case in this example, or is wiped dry as was done in Example 17. Therefore, it is apparent that the polyamide is plasticized by saturating it with water and that the water cannot function as a lubricant during compression rolling.

EXAMPLE 19 A commercially-obtained sheet of polystyrene having an average thickness of 5.0 mils was compression rolled satisfactorily using a lubricant. The following data were obtained:

Pressure, Percen temp., F. lbs. extension 200 50,000 0 H2O 200 50, 000 8 03% Aerosol/ 200 50, 000 14 H20. Do 10% Glycol/% 200 50,000 16 EXAMPLE 20 A commercially-obtained sheet of polytetrafluoroethylene having an average thickness of 5.0 mils was c0mpression rolled satisfactorily using a lubricant. The following data were obtained:

Roll Pressure, Percent Polymer Lubricant temp, F. lbs. extension Polytetra- None 170 2, 000 95 fiuoroethylene.

Do .03% Aerosol] 170 2, 000 113 170 2, 000 125 Do Silicone 170 2, 000 120 EXAMPLE 21 A sheet of cellulose acetate butyrate was prepared by extruding the cellulose acetate butyrate from a clear melt to form a sheet having an average thickness of 4.6 mils. The sheet was satisfactorily compression rolled using a lubricant with the results disclosed in the following table:

A polyacetal polymer resin obtained commercially was extruded to form a sheet having an average thickness of 38 mils. This material was satisfactorily compression rolled as shown in the following table:

Roll Pressure, Percent Polymer Lubricant temp, F. lbs. extension Polyacetal None 200 18, 000 182 .03% Aerosol] 200 15, 000 469 EXAMPLE 23 A commercially-obtained sheet of polyvinyl chloride having an average thickness of 10.1 mils was compression rolled satisfactorily using a lubricant. The following data were obtained:

Roll Pressure, Percent Polymer Lubricant temp., F. lbs. extension Polyvinyl None 200 5, 000 83 chloride.

H20 155 6,000 116 .03% Aerosol] 175 1 9, 000 116 165 1 9, 000 102 155 6, 000 124 125 5, 000 102 Octyl 200 5, 000 88 Phthalate/ 90% isopropanol. d0 155 6, 000 93 ..d0 155 9, 000 126 EXAMPLE 24.ANTIOX[DANTS Strips of unstabilized polypropylene were compression rolled from 24 mils to 8 mils thickness at a roll temperature of 2.00 F. After 42 hours under an ultraviolet lamp, a dry rolled strip had an inherent viscosity in tetralin of 0.50. A strip rolled with an isopropanol lubricant containing 8% 4,4-thiobis(6-tertiary butyl 3-methyl phenol) had an inherent viscosity of 1.31 after the same exposure.

EXAMPLE 25.ANTIBLOCKING AGENTS An extruded polypropylene strip was dry rolled from 20 mils to 5.5 mils at a roll temperature of 200 F.; a strip of the same thickness was rolled to 5.0 mils using an isopropanol lubricant containing 24% Armid O (oleamide). A block test similar to ASTM 88448, in which the samples were heated 16 hours at 81 C. under a 5 p.s.i. load, rated the dry rolled sample as blocking badly and the lubricated sample with Armid O (oleamide) as no block.

EXAMPLE 26.ANTIBLOCKING AGENTS An extruded polypropylene strip was dry rolled from 20 mils to 5.5 mils at a roll temperautre of 200 F.; a strip of the same thickness was rolled to 5.0 mils using an isopropanol lubricant containing diatomaceous earth in dispersion. A block test in which the samples were placed under a 1.0 p.s.i. load for 380 hours at room temperature rated the dry rolled sample as blocking and the lubricated sample with diatomaceous earth as no block.

EXAMPLE 27 .SLIP AGENTS The rolled strips of Example 25 were subjected to a slip test that measured the force in grams necessary to slide the sample across itself. A slip test result of 15 was obtained on the dry rolled sample and 7 on the sample rolled with Armid O (oleamide) in isopropanol.

EXAMPLE 28 Various additives including stabilizers, inhibitors, slip agents, antiblocking agents, surface modifiers, moistureproofing agents and the like are incorporated in the lubricants and the polyolefins shown in the above examples compression rolled and stress set to obtain transparent polymeric films. The haze measurements as expressed in percent total scattered light are in no way changed significantly due to the presence of the incorporated addi tives, nor are the other characteristics such as the percent extension, tear strength, modulus or moisture vapor transmission affected adversely by the incorporation of the additives in the lubricant.

EXAMPLE 29 Haze and extension determinations as follows were made on medium density polyethylene (0.93 gram per cc.). Films were compression rolled at a roll temperature of F. using film extruded from a clear melt onto a chilled roll.

Thickness Percent Original after so thickness, rolllng Percent tered Lubricant mils mils extension light;

Butyl acetate 4. 5-5. 0 1. 01. 5 280 1. 57 Hexane 4. 5-5. 0 1. 5 2. 7 3. 20 Xylene 4.5-5. 0 1. 5 217 3. 44 Butyl alcohol 4. 5-5. 0 1 5 217 1. Water with wett g agent 4. 5-5. 0 1. 5 217 2. 13 Methyl alcohol 4. 5-5. 0 1. 5 217 1. 60

When additives are incorporated in a lubricant sufliciently to improve the surface, to stabilize and to inhibit the polyolefin, the percent scattered light is found to remain substantially the same.

EXAMPLE 30 Maximum extension values were determined as follows from medium density polyethylene (0 .93 gram per cc.) extruded as in Example 29.

Whenever additives such as stabilizers and inhibitors are incorporated in the lubricants sufficient to incorporate about .011.0% by weight of the additive, the physical properties of the polyolefin are the same as when the samples are compression rolled using the lubricants without having the incorporated additives.

The crystalline structure of the film may be determined by X-ray diffraction patterns as is well known in the art. In the event that stretching is desirable, the polymeric film may be stretched in a direction laterally perpendicular to the direction in which the compression rolling takes place. The stretching step may be carried out using customary tentering equipment or it may be obtained by extruding plastic tubing which is extended laterally by causing the tubing to 'be filled with a fluid such as air, water or the like. In one embodiment of our invention, the polymer is extruded as a tubing into a water bath and stretched by having a liquid contained inside the tubing, which is preferably of greater density than the water.

A roll stack may be used which would eliminate the extruder where pellets are used which are converted into film by masticating rolls, then rolled down and relaxed on successive rolls in the stacks.

The pressure rolls have a pressure of at least'100 pounds per linear inch depending upon the polymer measured along the line where the sheeting passes between the two rolls. In other words, if 6-inch long rolls were used, the pressure exerted by the rolls, if the pressure were 300 pounds per linear inch, would be 1,800 pounds total pressure exerted by the rolls. In the event that the polymeric film is an amorphous polyester, it may be stretched in one direction at temperatures of 70105 C. and then rolled in a direction substantially at right angles to the direction of stretch in a rolling mill at temperatures of 80-150 C. using a lubricant. The film may then be heat-set at a temperature of l50250 C. while shrinkage of the film in any direction is prevented by maintaining the film under tension in the two directions.

Instead of a step requiring stretching in one direction, the polymeric film may be rolled in two directions by passing the film through the pressure rollers in a direction substantially diagonally so that the pressure rolling can be obtained in directions substantially perpendicular to each other. For small sections, however, the film may be rolled in one direction and then a section removed for rolling in a transverse direction.

A satisfactory method for measuring the second-order transition temperature is dependent upon the change in the specific heat of the polymer at that temperature. If a polymer is heated at a constant rate beginning at a temperature below its second-order transition temperature, the temperature will increase at a constant rate until the transition temperature is reached, at which point a break in the curve will occur. The determinations are made by placing the insoluble polymer with either normal-heptane or toluene at a temperature around 60 C. in a calorimeter. A constant rate of heating is obtained using an electrical heater connected to a voltage source which may be varied at will. The powdered polymer is kept suspended by an electric stirrer turning at constant speed. Temperature is measured by means of a copper-constantan thermocouple with an ice water reference point. After the calorimeter has reached equilibrium, the current is turned on so that the temperature will rise about 1 C. per minute. The zero time reading is selected at least C. below transition temperature. Thereafter, the lapse time is read off a stop watch to the nearest V of a minute for every 16 degree Centigrade rise. After going 1020 C. higher tha the inflection point, as noted by the data, the information is plotted on the graph.

The polyethylene or similar polymer may be used direct from the polymerization autoclave in the melt form to make sheeting and then compression rolled.

Cellulose esters and other highly crystalline polymers do not require a high percentage extension. Possibly 5% extension would be suflicient to provide orientation.

This procedure could be modified to extrude the film directly into the nip of the pressure rolls and quench the film with the lubricant at the instant the sheet contacts the rolls at the nip. This variation would be most effective for fabricating films of polymers which cannot be quenched to amorphous structures by practical procedures. The melts of such polymers are essentially amorphous but recrystallize readily when cooled and frequently become translucent or opaque over a narrow temperature range, which will be referred to as the frost-line. A sheet of such polymers could be extruded as a clear melt directly into the nip of the pressure rolls which would be flooded with lubricant maintained at the frostline temperature. Orientation and crystallization would occur simultaneously in this process which is the preferred sequence for most polymers. This would also make possible the fabrication of thin gauge films without drawdown or extension by drafting.

From the foregoing it is apparent that the use of a lubricant film on a polyethylene sheet as it is being rolled results in the sheet undergoing a substantially larger percent extension than can be produced it the sheet is rolled without a lubricant. It is also of major importance that the use of such a lubricant permits an extremely thin finished sheet to be produced in one pass through the rolls with substantially less roll pressure than was heretofore thought possible. However, perhaps the most surprising and important feature of this invention is the optical clarity of the finished film. Thus, this invention which teaches how a limp and cloudy polyolefin sheet material can be transformed in one pass through a low pressure compression roll into a thin, crisp, ultra-clear sheeting through the use of a lubricant on both sides of the sheet represents a substantial step forward in the polyolefin sheeting field.

What is claimed and desired to be secured by United States Letters Patent is:

1. A transparent polyolefin film having a modulus above l.0 10 pounds per square inch and a haze value of less than 3%.

2. A transparent polyolefin film according to claim 1 wherein said polyolefin is medium density polyethylene having a density of from 0.93 to 0.945 and its modulus is above 2.0x 10 pounds per square inch.

3. A transparent polyolefin film according to claim 1 wherein said polyolefin is high density polyethylene having a density of from 0.946 to 0.97 and its modulus is above 2.5 10 pounds per square inch.

4. A transparent low density polyethylene film having a density of from 0.91 to 0.929 and a modulus above 1.0 10 pounds per square inch, a haze value of less than 3%, and which at a thickness of 2.5 mils has a moisture vapor transmission rate of about'.20 gram per square inches of surface in a 24 hour period.

5. A transparent medium density polyethylene film having a density of from 0.93 to 0.945 and a modulus above 2.0 10 pounds per square inch, a haze value of less than 3%, and which at a thickness of 2.5 mils has a moisture vapor transmission rate of about .15 ram per 100 square inches of surface in a 24 hour period.

6. A transparent high density polyethylene film having a density of 0.946 to 0.97 and a modulus above 2.5 10 pounds per square inch, a haze value of less than 3%, and which at a thickness of 2.5 mils has a moisture vapor transmission rate of about .10 gram per 100 square inches of surface in a 24 hour period.

17 18 7. A polypropylene film having a modulus at about 3,194,863 7/1965 Williams et a1. 264175XR 3.5)(10 pounds per square inch in its lengthwise direc- 2,367,173 1/1945 Martin 264210 tion, a modulus of about 3.5 in its widthwise direction, 2,631,954 3/1953 B i ht 264 175 XR and a haze value of less than 3%.

5 PHILIP DIER, Primary Examiner References Cited U.S. Cl. X.R.

UNITED STATES PATENTS 3,037,862 6/1962 Neth 11734 XR 9687; 117-34, 138.8; 161-247; 264210 

